Tides are the winds of the oceans, generating a tremendous amount of kinetic energy that can be tapped with the right kind of technology. In fact, tides might be better than wind, since they're much more predictable. And while the best wind resources tend to be located far from major population centers, most of the big cities around the world are located right next to the water. The problem has always been that building turbines and other infrastructure is significantly more expensive underwater than on land, since salts can erode equipment and maintenance is a challenge.

That's still the case, but tidal power is slowly beginning to gain acceptance. The technology works the same way a wind turbine does: the steady movement in and out of the tide sturns an underwater turbine, which generates electricity. And as with wind,there are some parts of the world that are particularly rich in tidal potential, like the Bay of Fundy in Canada, home to some of the most intense tides on the planet. New York City's tides are a lot calmer, but the city does have potential for tidal power, and companies like Verdant are tapping it.